/Engine/Source/Runtime/Slate/Public/Widgets/Input/SComboBox.h
Handle case where user clicks on an existing selected item
virtual [FReply](API\Runtime\SlateCore\Input\FReply) OnMouseButtonDown ( const [FGeometry](API\Runtime\SlateCore\Layout\FGeometry) & MyGeometry, const [FPointerEvent](API\Runtime\SlateCore\Input\FPointerEvent) & MouseEvent )